Generally, in an optical design for an imaging optical system (hereinafter simply called an optical system) such as an imaging lens for a camera, optimization is carried out in such a manner that aberrations become optimum in a visible light range of the wavelength from about 400 nm to 700 nm. For example, with using line spectra such as d-line (wavelength: 587.6 nm), C-line (wavelength: 656.3 nm), and g-line (wavelength: 435.8 nm) radiated from helium lamp, hydrogen lamp and mercury lamp, respectively, balance of aberrations at respective wavelengths is optimized so as to obtain maximum optical performance upon imaging by using white light. Moreover, upon manufacturing such an optical system, quality control has been carried out by measuring optical performance by means of deriving modulation transfer function (MTF) mainly from line spread function (LSF) (for example, see Japanese Patent Application Laid-Open No. 58-092927)
More recently, in order to further increase optical performance, quality control has been carrying out by measuring wavefront aberration. As for a method for measuring wavefront aberration, other than an interferometer method that light transmitted through a test lens makes interference with light reflected from a reference surface having a given shape, obtained interference pattern is detected by a two-dimensional imaging device such as a CCD, an output signal from the two-dimensional imaging device is calculated, and wavefront aberration on a pupil of the optical system is derived, a Shack-Hartmann method attracts attention. The Shack-Hartmann method is a method that wavefront transmitted through a test lens is incident on a microlens array, in which a large number of minute microlenses (rectangular lenses) are disposed two-dimensionally, and divided by the microlens array into a large number of spot images formed on a two-dimensional imaging device such as a CCD, and local inclinations of wavefront are calculated from lateral shifts of the spot images detected by the two-dimensional imaging device, and wavefront aberration as a whole is derived (for example, see Japanese Patent Application Laid-Open No. 2005-098933). In a wavefront aberration measurement according to the Shack-Hartmann method, although transversal resolution is limited by the dimension of each micro-lens in comparison with the interferometer method, dynamic range for the measurement is extremely wide, so that the method is particularly suitable for wavefront aberration measurement of an optical system having large amount of remained aberrations such as an imaging lens for a camera.